This study of hormonal regulation of membrane function is targeted to provide the information needed to understand the mechanisms whereby age-dependent perturbations in physiological control systems lead to the inability of the organism to maintain homeostasis. Investigations are focused on the biochemical interactions of hormones, mediated via cyclic AMP and cyclic GMP, with membrane systems. Topics investigated include: 1) hormone receptors in membranes; 2) adenylate cyclase and guanylate cyclase activities; 3) phosphorylation of membrane proteins by cyclic nucleotide-dependent and -independent protein kinases; 4) control of cyclic nucleotide levels by regulation of phosphodiesterase activities.